Test of law of inverse squares 275 



As it might be suspected that in the principal experiment the neighbourhood 

 of the hemispheres communicating with [the] ground would enable the globe 

 to hold more than it would otherwise do, and that therefore the cork balls 

 would not separate so much as they would do if the hemispheres were taken 

 away and the quantity of redundant fluid in the globe was the same, and 

 consequently that the above computation of the quantity I could perceive is 

 not just, I took away the hemispheres, made the corks touch the globe, and 

 electrified it till they separated, then holding the hemispheres in my hands as 

 near the globe as in the experiment, I did not perceive any alteration in the 

 separation of the corks. 



The outside diameter of the hemispheres was 13-3 inches. 



563] Experiment to see whether the force with which two bodies repel is as the 

 square of the redundant fluid in them*: tried with straw electrometer and glass globes. 



The two electrometers were hung at opposite ends of a horizontal stick of 

 wood 43 inches long, supported on sticks of waxed glass and communicating 

 near the middle with one of the globes f. The same string also which lifted up 

 the electrifying wire let down a piece of wood for making a communication 

 between the two globes. The board with divisions was placed 6 inches behind 

 the electrometers, and the guide for the eye 30 inches before it. 



The electricity of the globes wasted very slowly, so that it could not be 

 sensibly diminished in the time between reading off divisions to heavy electro- 

 meter and those to light one. 



The electrifying wire rested on horizontal wood while globe f was turned, 

 two jars being used as a magazine to prevent the globe Leyden vial from charging 

 too fast. The globe J was turned till the heavy electrometer separated to rather 

 more than the intended division, after which I waited till it came right, when 

 by the string I lifted up the electrifying wire and made the communication 

 between the two globes and looked at the division of light electrometer. The 

 electricity of the magazine was discharged as soon as the electrifying wire was 

 lifted up. 



564] One of the straws used for the heavy electrometer was black in some 

 places, and is called "blighted," the other is called "fair." 



Sun. Jan. 24 [1773]. 



* [See Art. 386.] 



t [The coated globes 2 and 3. Their charges are given in Art. 505 as 1782 and 

 1555 circ. inc., or 1159 and 1009 glob, inc., the sum of which, 2168, agrees with 

 Art. 391.] 



J [Of Nairne's electrical machine.] 



1 8 2 



